In a cosmetic application, the topical delivery of skin actives into a deep skin layer, i.e., across the stratum corneum to the dermal layer, is oftentimes desired. However, an intact skin poses a major obstacle to the delivery of skin actives through the stratum corneum. The stratum corneum consists of corneocytes embedded in a lipid matrix composed of organized lipid bi-layers, where the lipid materials act as extra intercellular glue sealing the spaces between the cells in the stratum corneum.
In order to deliver skin actives across the intact skin, several approaches have been developed. One of them is to either destroy or fluidize the lipid bi-layer in the stratum corneum using hydrophobic medium such as the oil phase in an emulsion, thereby enhancing the penetration of actives.
Another approach is the use of a vesicular system such as liposomes. Liposomes are vesicles composed of phospholipid bi-layers. A phospholipid molecule has a polar “head” and two non-polar “tails”. Due to its structure, the phospholipid tends to form a vesicular bi-layer, i.e. liposome, with the polar heads of phospholipids aligning toward an outer or inner aqueous phase while the non-polar tails align toward each other. Such liposomes have been used to construct carriers for the delivery of actives.
However, effective entrapment of actives into a liposome and maintaining the stability of such a liposome may still be a challenge. It is known in the industry that the chemistry of to-be-entrapped actives affects the entrapment efficiency and associated loading rate of the actives into liposome. Hydrophobic actives comprising a carboxylate group, like glycyrrhetinic acid, pose such a challenge.
Therefore, there exists a need for a liposome into which hydrophobic actives comprising a carboxylate group may be formulated. The liposome should be stable and have a satisfying loading rate of such hydrophobic actives, and thereby have improved penetration into deep skin layer, and thus have improved residual amount of actives within skin layers.
While many others have sought to improve the liposome delivery of hydrophobic actives, the benefit of this present invention was not met and not disclosed in the art. See, for example, U.S. Pat. No. 5,569,464 relating to an aqueous dispersion for encapsulating hydrophilic or hydrophobic drugs, where the aqueous dispersion comprises a liposome, a hydroxyl acid, and an amino acid as a stabilizing agent, and EP patent 0211647 B1 relating to a liposome-forming composition comprising a hydrating agent and liposome-forming materials.